The present invention relates to packet data handling in a radio communications network. More specifically, the present invention relates to efficient handover of a packet data connection in a radio telecommunications network.
In release 6 of the 3GPP specification, packet-switched (PS) handover was introduced within the GSM Evolved Radio Access Network (GERAN) and between GERAN and the Universal Mobile Telecommunication System (UMTS) Radio Access Network (UTRAN). In the following, GERAN will be used to illustrate the different technical aspects and problems; however these aspects and problems are also valid in UTRAN as well as in other radio telecommunications networks of similar structure.
In GERAN, a Base Station System (BSS), or more generally a radio base station, also known as a Radio Network Controller (RNC) in UTRAN, handles the radio connection to radio terminals. The BSS, or Packet Control Unit (PCU) for packet data, is also connected to a Serving General Packet Radio Service (GPRS) Support Node (SGSN) for transferring packets to and from the radio terminal.
The SGSN is further connected to a Gateway GPRS Support Node (GGSN), which in turn is connected to other packet networks. Thus a packet-switched connection can be established between the radio terminal on one end and a packet-switched service located in a packet-switched network on the other end. Furthermore, the SGSN and the GGSN may be connected to other network nodes such as a Home Location Register (HLR) and the like.
The interface between the BSS and the SGSN is called the Gb interface and is specified in the Technical Specification 3GPP TS 48.018. The interface between two different SGSN nodes or between the SGSN node and the GGSN node is the Gn interface specified in 3GPP 29.060.
When a radio terminal sets up a packet-switched connection towards an access point, a Packet Data Protocol (PDP) context is established in the SGSN connected to the PCU serving the radio terminal, and in the GGSN serving the access point to which the radio terminal wishes to establish a connection. The PDP context contains information about the subscriber such as the radio terminal, and session information such as the IP-address, International Mobile Subscriber Identity (IMSI), Quality of Service (QoS), and the like.
In the SGSN, a Packet Flow Context (PFC) is associated with each PDP context. The PFC contains, amongst other things, information relating to the Quality of Service (QoS) that the packet connection needs to support. Based on this information, the PCU allocates more time slots, and schedules a user with higher QoS more often than a user with lower QoS.
Since resources in the radio interface are limited, and since a PFC consumes such resources, it is important to release these resources as soon as possible when they are not used. To this end, the PCU deletes a PFC whenever it is inactive for a certain time to conserve radio resources. When the subscriber once again receives or transmits packet data, a new PFC for the particular PDP context is once again set up.
Thus, the PCU has a timer for each PFC which is reset for each received packet, and if the timer lapses, that is, if there is no activity for a particular PFC for some time, the PCU may delete that particular PFC to save radio resources. This deletion is not reported to the SGSN.
When handover of the radio terminal is required due to changing radio conditions, the SGSN instructs the target PCU to set up PFCs corresponding to all PDP contexts that are active. This includes those PFCs that the source PCU has inactivated or deleted, but for which the corresponding PDP context is alive, since the SGSN has no knowledge of which PFCs are currently active. This process results in a non-optimal resource utilization in the target PCU.